As a method of depositing material particles having various functions to the surface of an object to be treated, a method of interposing an adhesive, a method of coating in the form of a paint, etc. have been known. However, in the methods described above, functional material particles are eventually covered by the adhesive, for example, to result in hindrance of the function at the surface thereof.
For instance, a catalyst or the like can provide a function efficiently by making the particles of crystal as fine as the material particle. However, most of them are buried in the adhesive, causing functional failure in the methods described above.
Accordingly, there has been a need for technical means capable of depositing fine material particles, for example, oxide crystals with no alteration for the function thereof, without using the adhesive or the like.
On the other hand, as a method of depositing various kinds of material particles to the surface of an object to be treated, a warm spray method of heating particles to a temperature lower than the melting point thereof and depositing them by blowing at a supersonic velocity has been known. According to the warm spray method of the type described above, since the modification of the surface of the object to be treated can be completed by blowing and depositing the particles to the objective, the method has attracted attention due to the superiority in view of various operations, for example, that the modification operation can be done in the field.
Then, also for the deposition of the functional material particles, it may be considered to apply a coating method by warm spray. However, deposition of the particles by the warm spray method with no alteration in the functionality has not been considered.
As the specific subject of the coating method by warm spray, voids tend to be formed in a case of blowing particles and, accordingly, a device has been made for decreasing the particle diameter as small as possible. However, it has been found that limits are imposed on the fineness of the particle diameter due to a jet pressure upon spraying.
Accordingly, there has been a need for technical means of overcoming limitations on the particle diameter and forming a dense layer with no substantial voids.